1. Field of the Invention
The present invention generally relates to a vacuum processing chamber. More particularly, the present invention relates to an apparatus comprising getter material for removing undesirable gases in a processing chamber.
2. Background of the Related Art
Substrate processing is usually carried out in vacuum processing chambers, such as physical vapor deposition (PVD) chambers, chemical vapor deposition (CVD) chambers and etch chambers. These vacuum processing chambers typically require high vacuum levels on the order of a few milliTorr to ultra high vacuum levels on the order of 10.sup.-9 Torr. Several pumps are usually connected in series or in parallel to the chamber exhaust to achieve the ultra high vacuum levels within a chamber. High pressure pumps, such as mechanical pumps, are often used first to reduce the pressure within the chamber to high vacuum levels of less than 1 Torr. Low pressure pumps, including molecular pumps, ion pumps, cryopumps, turbo pumps, and other vacuum pumps, are then used to reduce the pressure to ultra high vacuum levels. The pump-down time for a particular chamber can range from a few minutes to hours to days depending upon such factors as the size of the chamber, the capacity of the pumps, the conductance from the chamber to the pumps and the desired final vacuum level.
Getter pumps have been used in conjunction with other pumps to achieve high or ultra high vacuum levels. A getter pump generally includes a getter material (i.e., a metal alloy) which has an affinity for certain gases and is typically encased in a pump housing attached to the chamber. Getter materials can preferentially adsorb certain gases, but typically not the noble gases, depending upon the composition and the operating temperature of the getter material. U.S. Pat. No. 5,238,469, hereby incorporated by reference in its entirety, describes getter materials used for preferentially adsorbing selected gases. While many gases may cause undesirable depositions in semiconductor devices that change, for example, the resistivity, uniformity, stress, and reflectivity of the deposited films, oxygen and its various compounds appear to be primary causes of contamination during substrate processing. Other typical contaminant gases include water vapor and hydrogen. The contaminant gases are typically introduced into the processing chamber along with the process gases through the process gas inlets and/or manifolds. Another source of contaminate gases is the substrate itself, in which the contaminate gases are released or desorbed from the substrate in the processing chamber. The contaminant gases may form oxides on the substrate surface and on the surfaces of other components exposed to the process cavity. For example, in a PVD chamber, the contaminant gases may cause formation of oxides on the metal target surfaces, such as aluminum oxide on an aluminum target, resulting in unsatisfactory deposition and defect formations on the substrate.
Getter pumps can be configured to selectively adsorb the particular contaminant gases. Typically, a getter pump is attached externally to a vacuum processing chamber. U.S. Pat. No. 5,324,172, by Manini et al., entitled "High Capacity Getter," which is hereby incorporated by reference in its entirety, describes an external getter pump and a variety of getter materials that can be used with the getter pump. The getter pump described by the '172 patent is attached externally to the process chamber, and the effectiveness of the getter pump is restricted by the conductance between the getter pump and the chamber interior. Typically, the conductance between the getter pump and the chamber interior is controlled by the size of the chamber outlet and the getter pump inlet. Because of the physical location of the getter pump and the conductance limitation, the '172 getter pump is inefficient in removing undesirable gases from the process chamber. Furthermore, the '172 getter pump is unable to prevent the undesirable gases from contaminating the substrate surface during the deposition process because the '172 getter pump removes the undesirable gases from a location outside of the process cavity, after the substrate and other surfaces of the chamber components have already been exposed to the undesirable gases.
To address some of the problems encountered in using an external getter pumps, U.S. Pat. No. 5,685,963, Lorimer et al., describes a wafer processing system having a getter pump disposed inside a processing chamber for pumping an undesirable gas within the processing chamber. The processing system also includes a low pressure pump attached externally to the process chamber capable of maintaining a desired processing pressure within the processing chamber. The '963 getter pump is disposed within the processing chamber to adsorb an undesirable gas during processing and to eliminate the conductance problems experienced with externally attached getter pumps. Although the '963 getter pump provides better adsorption of undesirable gases than an external getter pump because the '963 getter pump is located within the processing chamber, the '963 getter pump still does not prevent the undesirable gases from reaching and contaminating the substrate surface and other chamber component surfaces, such as a target surface, during processing. The undesirable gases are still able to travel to the substrate surface and other chamber component surfaces, without first encountering the '963 getter pump, thereby contaminating these surfaces during the deposition process and cause defect formations on the substrate. Furthermore, because the '963 getter pump is bulky in construction, a larger internal chamber space is required to accommodate the '963 getter pump, resulting in a longer pump-down time.
Therefore, there remains a need for a substrate processing system that prevents the undesirable gases from contaminating the substrate deposition surface and surfaces of chamber components. Particularly, there is a need for an in-situ getter that reduces the undesirable gases from the process cavity and improves the properties of the deposited film by reducing the substrate surface contamination from undesirable gases during processing.